At the heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk rotates, air adjacent to the disk surface moves with it. This allows the slider to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Typically magnetic disk drives have been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Data density requirements are fast approaching the physical limits, however. For example, increases data capacity requires decreased bit sizes, which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write head technologies is reaching its physical limit.
One means for overcoming this physical limit has been to introduce perpendicular recording. In a perpendicular recording system, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. This flux then flows through the relatively magnetically soft underlayer and returns to the surface of the disk at a location adjacent a return pole of the write element. The return pole of the write element has a cross section that is much larger than that of the write pole so that the flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the flux too week to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.
It will be appreciated by those skilled in the art that the high coercivity of the disk surface material can make it difficult to magnetize, especially at increasingly small magnetic grain sizes. It has been found that angling the magnetic field slightly can improve transition sharpness and achieve better media signal to noise ratio. A proposal to achieve this has been to place a trailing shield near the write gap and magnetically connected with the return pole. The shield would in effect attract field emitted from the write pole, thereby angling it slightly.
A challenge encountered with this approach is that some field is lost to the shield, and increasing write field to compensate for this can lead to adjacent track interference due to stay fields. In other word, using a trailing shield to angle the magnetic field emitted from the write pole advantageously decreases the switching field necessary to make the perpendicular magnetic transition, increasing the speed with which data can be written. However, this improvement in switching field comes at the cost of lost magnetic field. This is because some of the field leaks to the shield (in a direction parallel to the disk surface) resulting a weaker field being emitted by the write pole. Therefore, there remains a strong felt need for a mechanism for canting the magnetic field of a perpendicular write pole, while minimizing field loss. In addition, a mechanism for doing so would have to manufacturable in a mass production setting to practicable.